This study will investigate pathogenetic mechanisms which are important in the generation of lesions caused by canine parvovirus (CPV). The effects of two routes of inoculation, intravenous and oral, will be compared in conventional and specific pathogen free (SPF) dogs. The sequential development of lesions, and their relationship to clinical disease will be studied. The magnitude of viremia will be quantitated and correlated with the distribution and severity of lesions. The sequential distribution of CPV in tissues will be studied by immunofluorescence and culture and the relationship between infection of lymphoid tissues, in particular, and the development of viremia determined. The antibody response to CPV infection, and its role in modulating viremia, will be studied. Further studies of the importance of the magnitude of viremia in this infection will be carried out by infecting dogs with widely varying doses of virus. The consequences of neonatal infection will be studied by inoculating newborn, seronegative puppies with CPV and determining the distribution of virus and the development of lesions.